1. Field of the Invention
This invention is related to recovering the ballast control in a wireless lighting control network when the main controller (master) fails. More particularly, this invention is related to a wireless lighting control network system and method in which all lighting ballasts act as backups for a network master control unit. Most particularly, this invention is related to a system and method for a master-slave architecture for a wireless lighting control network that include all lighting ballasts as backup for a network master control unit such that there is no need for reconfiguration of the network or human intervention when a master fails or functioning of the master or slave ballasts is interrupted.
2. Description of Related Art
Traditional lighting has wall switches wired to the ballasts individually or in groups. If one of the switches fails, the ballasts that are controlled by other switches won't be affected. In wireless control, the on/off or light intensity is controlled by the signals transmitted from a remote table-top or handheld control unit via infra-red (IR) or radio frequency (RF) communication media.
There are basically two types of system configurations in wireless control. One is a distributed system that has several remote control units, each remote unit controlling a certain number of ballasts through the wireless links. The ballasts obtain the IDs of their designated controllers during the initialization of the system. Then, during normal operation the ballasts “listen” and react to the lamp operational signals coming transmitted by these controllers. The systems described in U.S. Pat. No. 5,848,054 to Mosebrook et al. and U.S. Pat. No. 6,174,073 to Regan, fall into this category.
The other type of system is a master-slave oriented networked architecture, which is the focus of this invention. There is one central device, so called “master” or “network coordinator” that manages communication among the network nodes. The ballasts and the remote controls both act as the slaves in the network. All the information about the wireless links between the keys on the remote control and the ballasts is gathered in a table stored in the master during initial configuration of the system. During the normal operation, the signal transmitted by a remote control is routed to its destination ballast by the master based on the link information in the table. The physical form of the master can be the same as a slave device, i.e. the master can reside in the remote control or the ballast. It is preferable to put the master in the ballast as it is mains-powered and at a fixed location. Connecting to the mains allows the master to transmit beacon packets that contain the master status information as a way to keep the slaves in touch every once in a while. Being at a fixed location avoids problems a missing handheld remote control since all the network information is lost in such a case.
The master-slave networked system has the following advantages over the distributed system:                If more than one remote-control is needed in a multi-zone office, a separate master is essential for network recovery if a remote control is lost.        A master-slave architecture centralizes the control information for the local network and makes it easier to form the building-wide network.        
In both wireless systems, there could be several reasons for a system failure:                Power Loss: In normal operation, the ballasts should not be cut off from the mains power for any reason, as they have to keep the RF communication alive all the time. Turning-off the lamps only puts the lamp-drivers in stand-by in digital ballasts, and it does not shut off the power supply to the circuits. Sometimes the controller that happens to be installed on a different mains power line from the ballasts experiences a power outage. Other times the controller could be running out of battery if battery powered.        Circuit malfunction: This includes circuit failures in the master control unit (MCU) or RF transceiver, and the temporary RF signal blockage/shielding or interference such that the communications between the devices are blocked.        Master Control Unit Failure: In a wireless network the master control unit represents a single point of failure. That is, once the master fails, all link information kept only by the master is lost. In a point-to-point network the network is no longer operable. This also occurs because the master routes all the packets and the master fails.        
There are several ways to enhance the reliability. The wireless system taught by U.S. Pat. No. 5,848,054 to Mosebrook et al., increases the reliability communications by adding repeaters between the source and destination devices. When the master and the ballasts suffer from intermittent communication in the direct path due to distance or RF interference, a repeater provides an additional communication path. However, this does not solve the problem of the master going completely dead.
Another system, taught by EP0525133 to Edwards et al., solves the master power outage problem by providing a battery as a back-up power source. When AC power is available, the battery is being charged. When the AC is cut off, the power supply automatically switches to the battery. Even though this idea teaches a battery backup for conventional hardwired lighting systems, it can be applied to the wireless system too. However, it can be costly to provide an additional power supply to every control device.
In a master-slave networked system, due to the important role of the master, it is critical to make sure that there is always a master working properly at all times. If the controller fails due to a power outage (dead battery) or malfunction, the problem arises of to how to regain controls of the ballasts. New replacements can be brought in, but the configuration, such as which key to control which ballasts, has to be set up again since there is no hardwiring in a wireless control system. Depending on how the wireless control network is built in the first place, sometimes this may mean starting the configuration from scratch all over again.